This invention relates to the field of processing of molten metals, and in particular to an apparatus for adding refining or alloying ingredients to improve properties of metal being processed.
In connection with the processing of molten metals, and in particular iron, steel and the like, it is known to add small amounts of elements such as calcium to the metal in its molten state in order to deoxidize and/or desulphurize the metal. Trace elements on the order of parts per million have substantial beneficial effects on the final product.
In metal processing, and in particular steel processing, molten metal generally is separated from a quantity of slag which remains relatively solid and floats upon the surface of the molten metal. The slag is made up of various lower-density impurities, quantities of oxidized metals and the like. In order to feed an additive material into the molten metal, the additive must be placed below or caused to pass through the slag surface. Unfortunately, merely feeding the material onto the surface of the molten metal in the form of a wire tends to accumulate unnecessarily high concentrations of the additive near the point of feeding and to waste a quantity of additive in the slag. Moreover, inasmuch as the additive material is not homogeneously mixed throughout the metal, a larger overall quantity of additive is required in order to reach the minimum concentrations required throughout the metal.
Addition of an additive material below the surface of a molten material involves certain considerations. Of course, an injection device must be employed which will not melt immediately when placed in the molten material. This having been accomplished, for example, by cooling the injection device and/or use of a refractory material, some provision must be made to prevent the solidification of molten metal on the surfaces of the injection device. In attempting to introduce material below the surface of molten metal through a feeding nozzle, the molten metal tends to enter the feeding nozzle and bind to internal nozzle portions, thereby stopping the feed.
Although it is known to treat processed steel with calcium in order to improve quality by reducing the effects of sulphur, it should be noted that steel processing is highly competitive in terms of cost. Many of the manufacturing processes are widely known and practiced in virtually identical form, such that a relatively minor difference in cost between producers is sufficient to swing a larger share of the demand to the lower cost product. Of course, additive materials intended to improve the properties of the steel are relatively expensive and must be conserved. Any waste of a calcium-containing additive material, for example by the loss of material in the slag layer during addition, has a major impact on the producer and the product. It is therefore highly desirable to feed the calcium well below the surface of the molten metal to the point where it will be most effective, and to mix the molten metal to evenly distribute the calcium additive therein.
The apparatus of the present invention is intended to facilitate the feed of additive materials, such as calcium-containing materials in the form of wire, to molten metals and is particularly suited for use in the method disclosed in the concurrently filed, copending, commonly assigned U.S. patent application of Joseph G. Kaiser entitled "Process for Adding Calcium to a Bath of Molten Ferrous Material", Ser. No. 522,754 filed Aug. 12, 1983.